Different types of circuits, for example sequential logic circuits, typically require what is normally referred to as a power-on reset in order to correctly begin their operation. The circuit is switched, in particular, to a defined state by means of a reset of this type. Without a reset of this type, circuits of this type may, for example, assume an undefined, for example random, state during power-on, which could result in an undefined operation.
Many commercially available integrated circuits therefore have a reset pin to which a reset signal can be applied by a user or under the control of other circuits in order to switch the integrated circuit to a defined state of this type. However, it is increasingly necessary for a circuit to power on in a defined manner even without an external reset signal. Internal reset signal generation circuits within the integrated circuit can be used for this purpose. These circuits typically respond to an event, such as an activation of a supply voltage, by outputting a defined signal as a reset signal. One example of a circuit of this type is known from U.S. Pat. No. 6,107,847 A. In the context of this application, circuits of this type are also referred to as POR (“Power On Reset”) circuits.
However, an internal reset signal generation circuit of this type is comparatively difficult to check and test. Even if, for example, the internal reset signal generation circuit has a fault, the circuit may nevertheless power on (“randomly”) in a defined state. Moreover, even if an internal reset signal is correctly generated when the circuit is tested, it may occur that no reset signal of this type is generated under certain operating conditions, which in turn may sometimes then result in an undefined power-on of the circuit. Faults of this type may thus be difficult to detect, and it may be difficult, in particular, to identify corresponding circuits as defective in which the internal reset generation does not operate correctly under all conditions. This is disadvantageous, particularly for safety-critical applications. For safety-critical applications of this type, is often necessary at least to be able to clearly detect when a circuit is not operating correctly, wherein the probability of an incorrect operation should preferably be as low as possible.
One object of the present application is therefore to provide devices and methods which are improved in this respect.